Mutant human Presenilins influence the proteolysis of amyloid precursor protein (APP), causing an accelerated accumulation of neurotoxic amyloid peptides in Alzheimer's disease. In the model organisms Caenorhabditis, Drosophila, and the mouse, Presenilins are required for Notch/Lin-12 developmental signaling. Presenilins regulate key proteolytic processing events during Notch receptor maturation and signaling that may be analogous to the Presenilin-dependent cleavages of APP in Alzheimer's disease. Presenilins have also been implicated in the cellular response to neurodegenerative apoptotic stimuli in both mammalian cells and Drosophila. In this FIRCA application, transgenic Drosophila will be generated that overexpress both wild-type and Alzheimer's disease-associated Presenilins. The functional properties of transgenic Presenilins will be assessed by several criteria, including analysis of developmental and adult phenotypes, interactions with Notch pathway genes, effects on Notch receptor processing, and induction of apoptosis. Human Presenilins (PS1 and 2) as well as human APP will also be functionally characterized in this transgenic model. These studies will be coupled with parallel tests of the wild-type and mutant proteins in mammalian neuronal cell culture to assess the degree of functional similarity between Drosophila and human Presenilins. The possibility that Presenilin genes are transcriptionally regulated by Notch signaling output will also be tested using these models. These studies will determine if Presenilin is a component of the feedback mechanism known to operate on the Notch pathway. Finally, Drosophila Presenilin mutants and other new mutants that interact with Presenilin will be systematically examined for adult learning and memory deficits, extending the developmental analysis of these mutants that is already underway. This well-defined set of proposed studies seeks to evaluate the utility of Drosophila as a transgenic model for functional analysis of human Presenilins, and to uncover conserved activities of fly and human Presenilins in apoptosis, neurogenesis, and neurodegeneration that occur during early development as well as during later learning and memory consolidation. The studies proposed here will clarify the in vivo activity of Presenilin in the processing of Notch, APP, and other proteins, and may ultimately increase our understanding of the molecular causes of Alzheimer's disease and its accompanying memory decline in humans.